The longterm objective of this proposal is in vitro production of insulin-secreting human B-cells in sufficient quantities to reverse diabetes in human patients after transplantation of cell masses or neoformed islets. The immediate aims outlined in this proposal are increases in neonatal rat B-cell production by supplementation of the culture medium with hormones and growth factors as well as by altering the substratum. B-cell proliferation and insulin secretory activity will be monitored by cell counting, radioimmunoassay, histology, electron microscopy, and immunocytochemistry. In vivo survival and function of cultured rat B-cells and islets will be tested in animals. Cultured B-cells and islets will be transplanted beneath the kidney capsule in experimental rats in the absence of immunosuppression. Treatments such as prolonged culture, high oxygen tension, or cloning of B-cells will greatly reduce, inactivate or eliminate rejection-initiating cells in the cultures. Graft viability will be assessed histologically in normal rats as well as functionally in streptozotocin-diabetic rats. Function of cultured B-cells and islets is monitored by reversal of diabetes. We anticipate to apply to fetal human B-cell cultures the methods learned from the rat model.